Electric motor vehicles including electric and hybrid vehicles that use a battery as a primary or secondary power source may have the battery charged regularly by, for example, a charge facility or an outlet power at home. The cruising range (i.e., a continuously travelable distance) of the electric motor vehicle is generally shorter than the cruising range of a gasoline engine vehicle. In addition, the time needed to re-charge the electric motor vehicle may take longer time than re-fueling the gasoline engine vehicle. Therefore, a user of the electric motor vehicle may be concerned about whether he/she will be able to reach a destination of travel without suffering from electric power shortage or whether he/she may miss an appointment due to re-charging.
Based on Japanese Patent Laid-Open No. 2010-286400 (JP '400), a navigation apparatus in the electric vehicle searches for a guidance route to the destination, predicts the travel time of the guidance route as well as the power consumption by the vehicular devices such as a headlamp and the like, and calculates/displays a travelable distance based on the currently-remaining amount of battery. Further, if it is determined that the currently-remaining amount of battery does not allow the vehicle to reach the destination, the navigation apparatus searches for a charge facility within the reach (i.e., the travelable distance), and notifies the driver of the searched facility.
In addition, excessive charging of the battery to have a more-than a required power amount is not only undesirable but is also harmful, in terms of charge, for example, cost and charge time. Thus, an accurate estimation of the amount of electric power needed in the battery is important.
Factors affecting the amount of power consumption include, for instance, a slope of a road. That is, an uphill slope may substantially increase the battery consumption than a downhill slope for the same distance of travel. However, in the disclosure of JP '400, an estimation of the battery power consumption does not consider the slope of the road in the course of estimating the battery power consumption for the guidance route, thereby not enabling the accurate calculation of the amount of electric power needed. If the road map data include a highly accurate slope data, the accurate calculation of the amount of electric power of the battery may be possible. However, the cost and time for preparing such data may be significantly large and may not be feasible.
Further, besides the slope of the road, other factors such as a vehicle weight may also affect the battery power consumption. That is, even when the vehicle is the same, the number of occupants and/or the weight of the load lead to the change of the total weight of the vehicle, thereby affecting the battery power consumption for the same route. Conventionally, such a change due to the total weight of the vehicle has not been considered.